The present application is directed to an interbody device for implantation between a pair of adjacent vertebrae in order to provide support to the vertebrae and/or promote bone fusion between the vertebrae and, in particular, to a non threaded interbody device having opposed concave sides and a solid core.
In the human spine the pad or disc between vertebrae is sometimes damaged or deteriorates due to age, disease, injury, or congenital defect. The vertebrae may also become compressed or otherwise damaged. Vertebrae often become too closely spaced anteriorly due especially to age and other factors that generally produces an abnormal and undesirable curvature with respect to lordosis or kyphosis. Because of this, surgery is sometimes utilized to place spacers or interbody devices between the vertebrae which provide proper spacing of the vertebrae and which also promote fusion between the vertebrae. When a device of this type is utilized for purposes of promoting fusion, it is often referred to as an intervertebral fusion device. When utilized to promote fusion, bone pieces or bone growth promoting material is normally packed or placed between the vertebrae to promote growth of bone and, therefore, fusion between the vertebrae.
In the past, interbody devices have typically had a hollow central cavity and been either generally rectangular in shape or cylindrical in shape and threaded. The cylindrical devices also typically have passthrough perforations or fenestrations and are threadably received between as well as into the adjacent vertebrae. For placement of cylindrical devices, the vertebrae are typically first spaced apart to a desirable position, and then a drill is utilized to create a partial bore (radiused channel) in each vertebra which allows this type of interbody device to be received in the space between the vertebrae and partially into each vertebra. Because of the space between the bones, the interbody device usually engages the bones only along an upper surface and a lower surface thereof. When the interbody device is of a cylindrical threaded type, the upper and lower surfaces are radiused relative to a front to rear axis and such are essentially designed to engage the region of the vertebrae where bone is unremoved by boring. Such devices obviously require removal of bone, but it is preferred that the vertebrae be left as whole as possible so such removal is not desirable.
However, when interbody devices are used, it is desirable that the device engage as much surface of bone as possible to provide support to the bone and to reduce the likelihood of subsidence of the device into the bone. Such subsidence results from contact pressure of the interbody spacer relative to an engaging surface of a vertebra, since part of the bone is somewhat spongy in nature, especially near the center of the upper and lower surfaces of the bones. The remainder of the interbody device mainly functions to support the two surfaces. Because it is also desirable in such structures to maintain weight and volume as low as possible, in order to make the device more compatible with the body, it is also desirable to make the entire device as small and lightweight as possible, while maintaining strength. In the present application this is accomplished by use of a solid core with side surfaces that are concave facing laterally outwardly so as to produce upper and lower arches on each side that provide effective and efficient load bearing buttress structures that better distribute overall implant stresses thereby providing strong support to the vertebrae with comparatively less implant weight and volume.
As noted above, it is also desirable to minimize the amount of cutting into and reshaping of the vertebral bones to only that which is necessary to correct the structure and function of the spine. Thus, it is considered advantageous in the present invention to conform the interbody spacer to the shape of the intervertebral surfaces of adjacent vertebrae, which is shallowly concave, rather than conform the vertebrae to the shape of the interbody spacer.
As noted above, age and injury cause the vertebrae to somewhat anteriorly collapse over time. Therefore, it is preferred that such an interbody spacer correctly space the vertebrae anteriorly so as to promote normal lordosis or curvature with respect to the spine in the lower back or kyphosis in the upper back.